Method and device for controlling the opening of an intake valve of an internal combustion engine

ABSTRACT

A method for controlling the opening of at least one intake valve of a combustion chamber in a periodically working piston engine, at least one intake valve of the combustion chamber being opened during a first partial period of a working period of the piston engine for charging the combustion chamber; and at least one intake valve of the combustion chamber being opened during a second partial period of the working period, wherein the second partial period begins after the combustion of the combustion chamber charge and has no overlap with the first partial period.

FIELD OF THE INVENTION

The present invention relates to a method and a device for controllingthe opening of at least one intake valve of a combustion chamber of aperiodically operating piston engine, at least one intake valve of thecombustion chamber being opened during a first partial period of aworking period of the piston engine for charging the combustion chamber,and at least one intake valve of the combustion chamber being openedduring a second partial period of the operating period.

BACKGROUND INFORMATION

European Patent document no. 473 258 A2 refers to an intake valve thatis opened twice during one working period. The first opening begins inthe range of the top dead center of a piston and ends in the intakestroke during the downward movement of the piston.

The second opening begins at or after the lower dead center of thepiston, at the beginning of the compression stroke, and ends before theend of the compression stroke. The exemplary method is used at low loadsof the internal combustion engine, which are distinguished by a lowcharge of the combustion chamber with combustible mixture. This slightquantity may be sucked in already using a relatively short first openingof the intake valve. Therefore, the intake valve may be closed beforethe end of the intake stroke.

Because of the piston running further in the direction of the bottomdead center while the intake valve is closed, a decreasing pressure isgenerated in the combustion chamber, whose absolute value undershootsthe intake manifold pressure. Because of this pressure drop, upon thesecond opening of the intake valve in the bottom dead center or afterthe bottom dead center, additional air or additional mixture flows intothe combustion chamber. The flow brought on by the pressure drop causesa desired turbulence in the combustion chamber, which improves thepreparation of the mixture for the subsequent combustion.

To the extent that this involves the heating of a catalytic converter inthe exhaust gas of the internal combustion engine, this documentsuggests an earlier opening of the exhaust valve in the combustionstroke, because in this way less energy would be converted to mechanicalwork, and as a result, the exhaust gases would be hotter. In order toheat up a catalytic converter and to reduce hydrocarbon emissions aftera cold start of an internal combustion engine, frequently so-calledsecondary air is blown in after the exhaust valves of the internalcombustion engine. The secondary air is blown in as fresh air via anelectric pump, and it allows for the oxidation of uncombustedhydrocarbons in the exhaust gas that is still hot.

In this context, the internal combustion engine may be operated usingexcess fuel, so as to supply hydrocarbons as reaction partner for thesecondary air blown in. The post-oxidation of the hydrocarbons notcombusted in the combustion chamber using the blown-in secondary airgenerates an exothermic reaction in the exhaust gas system and allowsfor a rapid heating up of the catalytic converter.

In this context, one may differentiate between a reaction in the exhaustmanifold and a reaction in the catalytic converter. If a reaction isdesired in the manifold, the exhaust gas has to come together with thesecondary air as early as possible after the combustion of thecombustion chamber charge. Therefore, the location of introduction ofthe secondary air often lies directly at the exhaust valves of theinternal combustion engine.

Besides the classical injection of secondary air with the aid of anelectric pump, one may operate individual cylinders of an internalcombustion engine alternatingly using excess fuel and excess oxygen, inorder to achieve a secondary air effect upon guiding together theexhaust gas from the combustion with excess fuel with the exhaust gasfrom the combustion with excess air.

SUMMARY OF THE INVENTION

An object of the exemplary method and/or embodiment of the presentinvention is to provide a method and a device for a combustion enginehaving fully variable valve control, which allows for the supply ofsecondary air to the exhaust gas without using a secondary air pump or asecondary air valve. In this context, the quantity of secondary air isto be variable.

This object may be attained by the above method described herein inwhich the second partial period begins after combustion of thecombustion chamber charge, and does not overlap with the first partialperiod.

With the aid of the exemplary method according to the present invention,post-oxidation of uncombusted hydrocarbons may be achieved directly inthe combustion chamber. For this purpose, the intake valve is opened inthe expansion phase at the point in time at which the pressure in thecombustion chamber has approximately reached the manifold pressure orundershot it. The fresh air flowing, in this case, into the still veryhot exhaust gas takes care of a post-oxidation of uncombustedhydrocarbons. The quantity of secondary air may be varied by theselection of the valve lift and/or the closing time of the intake valve.Thereby one may save a secondary air pump and a secondary air valve. Theonly assumption is that the fully variable valve control provides foropening the intake valve twice per operating period. In this context,the first opening is used to fill the combustion chamber with air forgenerating the combustion chamber charge required for the torquedemanded, and the second opening is used for secondary air metering.

An exemplary method provides that the second partial period beginsbefore a bottom dead center of the piston appertaining to the combustionchamber. The pressure in the combustion chamber decreases with theapproach of the piston to the bottom dead center. Therefore one mayconclude what the pressure in the cylinder is, from the position of thepiston.

The triggering of the second partial period as a function of the pistonposition thereby may have the advantage that the point in time at whichthe inner pressure of the cylinder or the inner pressure of thecombustion chamber undershoots the intake manifold pressure may be givenwithout a special combustion chamber pressure sensor.

Another exemplary embodiment provides that the second partial periodbegins at that point when the pressure on the side of the intake valvethat faces the combustion chamber has sunk to the value of the pressureon the side of the intake valve facing away from the combustion chamber,or has even undershot it.

Another exemplary embodiment provides that the length of the secondpartial period and/or the degree of the opening of the intake valve is afunction of operating parameters of the piston engine.

Another exemplary embodiment provides that the charge of the combustionchamber is limited by an early closing of the intake valve, and that theexemplary method is carried out at the highest possible intake manifoldair pressure.

Another exemplary embodiment provides that the exemplary method iscarried out only below a threshold value for the combustion chambercharge. The reason is that, at large combustion chamber charges, at theend of the expansion stroke, the low absolute pressure in the combustionchamber/cylinder required for drawing in secondary air from the intakemanifold is not achieved.

Another exemplary embodiment provides that, in the case of a combustionchamber having a plurality of intake valves, at least one first intakevalve is opened during the first partial period, and at least one secondintake valve is opened during a second partial period.

The exemplary embodiment of the present invention also provides acontrol device for implementing at least one of the abovementionedmethods, embodiments and measures. One embodiment of this control unitprovides that the control unit will increase the idling speed of thepiston engine if one of the abovementioned methods, embodiments ormeasures is carried out. An increased idling speed lowers the fresh aircharge required for the idling. Therefore, by having an elevated idlingspeed, the abovementioned threshold value for the combustion chambercharge may be undershot. For, it has been shown that the exemplarymethod runs in a satisfactory manner only for fresh air charges of thecombustion chamber up to approximately 35% of the maximum combustionchambers charges.

At higher charges, the final expansion charge is not less than theintake manifold pressure. The hydrocarbon emissions then have to belowered in a different manner. At higher fresh air charges, thelean-mixture drivability of the piston engine is better. Therefore, atcombustion chamber charges above 35% of the maximum charge, the internalcombustion engine may be operated in an increasingly lean manner.

Another exemplary embodiment provides, also for decreasing the charge,that the control unit transfers the shifting points of an automatictransmission towards greater rotary speeds if a method for blowing insecondary air through an opening of an intake valve is to be carried outat the end of the expansion stroke. Therefore, the exemplary methodand/or embodiment of the present invention also relates to a controlunit that is distinguished by operating the piston engine in anincreasingly lean manner with increasing combustion chamber charge, i.e.using fuel/air mixture poorer in fuel, in the case of carrying out theblowing in of secondary air by opening an intake valve at the end of theexpansion stroke.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the technical environment in which the exemplary methodand/or embodiment of the present invention shows its effect.

FIG. 2 shows schematically an exemplary embodiment of a fully variablevalve control.

FIG. 3 shows an exemplary method according to the present invention inthe form of a flow chart.

FIG. 4 shows a modification of the subject matter of FIG. 3.

FIG. 5 shows the curve of a variable(s) plotted over time or plottedagainst the crankshaft angle, as it may appear during the execution ofthe exemplary method of the present invention.

FIG. 6 shows the curves of a variable(s) plotted over time or plottedagainst the crankshaft angle, as it may appear during the execution ofthe exemplary method of the present invention.

FIG. 7 shows the curve of a variable(s) plotted over time or plottedagainst the crankshaft angle, as it may appear during the execution ofthe exemplary method of the present invention.

FIG. 8 shows the curves of a variable(s) plotted over time or plottedagainst the crankshaft angle, as it may appear during the execution ofthe exemplary method of the present invention.

DETAILED DESCRIPTION

The number 10 in FIG. 1 denotes a piston engine having a combustionchamber 12 which is movably sealed by a piston 14. Combustion chamber 12is filled with air from an intake manifold 16 via an intake valve 18when the piston moves downwards. To the combustion chamber air charge,fuel is supplied via a fuel injector 20, and the fuel/air mixture thuscreated is ignited with the aid of a spark plug 22. The force on piston14 created by the combustion is converted to a rotary motion of acrankshaft via a crankshaft drive 24. A pulse-generating wheel 26 isrotatably fixed to the crankshaft, and it bears ferromagnetic markings28.

During the rotating motion of the pulse-generating wheel 26, theferromagnetic markings 28 brush past an inductive pickup 30, which formsfrom this a periodic electrical signal which it supplies to an enginecontrol unit 32 and to a valve control unit 34. Both engine control unit32 and valve control unit 34 are able to derive the position of thepiston from this, and are able to control the injection of fuel, thetriggering of the ignition as well as the operation of intake valves 18and exhaust valves 36 in a phase-synchronized manner with the movementof piston 14. Thus, for example, exhaust valve 36 is opened when piston14 is running upwards again, for expelling the combusted gases fromcombustion chamber 12.

An exhaust gas sensor 38, such as an oxygen-sensitive lambda probe or anNOx sensor or an HC sensor, supplies a signal to engine control unit 32,so as to control, for example, the lean operation desired in oneexemplary embodiment of the present invention. The combusted gases runthrough a catalytic converter 40, which converts NOx, CO and HC tonitrogen oxide, carbon dioxide and water, when it is in the hotoperating state.

FIG. 1 also shows a transmission control unit 42 and an automatictransmission 44. The three control units 32, 34 and 42 are connected viaa bus system 46, such as a CAN bus. It should be understood that thesubdivision of the functions to three control units that communicatewith one another by a bus is not essential, and that the requiredfunctional scope could also be covered by a single control unit havingthe equivalent capabilities. The function of the transmission controlunit relates to another aspect of an exemplary embodiment of the presentinvention. The control unit composite consisting of the engine controlunit and the valve control unit consequently represents an exemplaryembodiment of a device according to the present invention.

Besides the signals of inductive pickup 30 and exhaust gas sensor 38,additional variables are supplied to engine control unit 32, especiallythe signal of an air mass flow sensor 48 which records the mass of theair aspirated by piston engine 10, and an accelerator sensor 50 which,to an extent, supplies information concerning the torque demand by thedriver. Valve control unit 34 controls an intake valve actuator 52 andan exhaust valve actuator 54. Intake valve actuator 52 and exhaust valveactuator 54 may be implemented as electrohydraulic actuating elementswhich are connected to a high-pressure accumulator 56, which containshydraulic fluid.

FIG. 2 shows an exemplary embodiment of an intake valve actuator 52 oran exhaust valve actuator 54. Hydraulic fluid from high-pressureaccumulator 56 flows via a first magnetic valve 58 into chamber 60,opens intake valve 18 or exhaust valve 36 and displaces the hydraulicfluid in chamber 62. When the desired valve lift has been achieved,first magnetic valve 58 is closed by valve control unit 34. In order toclose intake valve 18 or exhaust valve 36, second magnetic valve 64 isopened. In this context, first magnetic valve 58 remains closed. Thepressure of the hydraulic fluid that is constantly present at chamber 62closes intake valve 18 or exhaust valve 36. Hydraulic fluid flowing outof chamber 62 is collected in a reservoir 66. With the aid of the valveactuator shown, individual control may be provided for each valve. Inthis context, the charge of the combustion chamber with fresh air may beset by the duration of being open and/or the lift of intake valve 18. Atleast at low rotary speeds, an intake valve may be opened several timesper operating period.

FIG. 3 shows a flow diagram as an exemplary method of the presentinvention, the way it may proceed in the composite of control units 32,34 and 42 that communicate via bus system 46. In this context, block 3.1represents a main program for controlling the piston engine, as it runswith respect to control, injection and ignition in engine control unit32, and as it runs with respect to control of intake valve 18 andexhaust valve 36 in valve control unit 34.

In a step 3.2 it is checked whether the triggering conditions forblowing in secondary air are satisfied. The triggering conditions aresatisfied typically when piston engine 10 has been started in the coldstate. If this is not the case, the program branches back to mainprogram 3.1. If, however, the blowing in of secondary air is to takeplace, then via marks A and B a step 3.5 is reached in which therelative charge of the combustion chamber or the combustion chambers iscompared to a threshold value. The threshold value must be constitutedin such a way that relative combustion chamber charges, which undershootthe threshold value, lead to a relatively low final combustion pressurein combustion chamber 12.

It has been shown that a threshold value of ca. 35% of the maximumcombustion chamber charge, achieved under normal conditions, suppliesthis property. If this threshold value is exceeded in step 3.5, theblowing in of secondary air according to the exemplary method and/orembodiment of the present invention cannot be carried out via an openingof the intake valve in the range of bottom dead center of the pistonafter combustion. In this case, alternatively the program may branch toan engine control program module in a step 3.6, which operates thepiston engine using a lean mixture to minimize hydrocarbon emissions.

In order to be able to carry out or performing the blowing in ofsecondary air using the exemplary method and/or embodiment of thepresent invention, piston engine 10 should be operated using lowcombustion chamber charges. This may be promoted by the sequence ofsteps 3.3 and 3.4 in FIG. 4. Therefore, these steps may be carried outin FIG. 3 between marks A and B that were mentioned.

For example, in a step 3.3 the idling speed may be lifted. An increasedidling speed lowers the fresh air charge required for idling. Invehicles having automatic transmissions 44, in step 3.4 the transmissionswitching program in control unit 42 may additionally be changed in sucha way that piston engine 10 is operated on the average with a higherrotary speed. Just as during idling, it is true in this case that theincreased rotary speed goes along with a reduced charge, whichsimplifies or allows for the triggering of the blowing in of secondaryair according to the exemplary method and/or embodiment of the presentinvention. If the combustion chamber charge is small enough, then instep 3.7 there takes place a determination of the piston position byevaluating inductive pickup 30. If the charge in the combustion chamberis known, one may conclude what the combustion chamber pressure is fromthe position of the piston. The closer the piston approaches bottom deadcenter in the combustion stroke, the larger becomes the combustionchamber volume above the piston, and the lower becomes the pressure inthe combustion chamber. In explaining the remaining steps 3.8 to 3.12,we first of all explain below various signal patterns.

FIG. 5 shows the curve of combustion chamber pressure for variouscrankshaft angle degrees, which correspond to various settings of piston14. The section marked 5.1 corresponds to a falling of the combustionchamber pressure during and after combustion. At the moment at which thecombustion pressure undershoots intake manifold pressure PS, a pressuredrop is created at intake valve 18, which may be used to have secondaryair flow in.

FIG. 6 shows the valve lift of an intake valve 18. In this context, thetips correspond to a fully open valve. The left valve opening in FIG. 6here corresponds to a second partial period. When intake valve 18 isopen, air flows from the intake manifold into combustion chamber 12,which permits the pressure in the combustion chamber to rise to thevalue of the intake manifold pressure. This shows in the curve ofsection 5.2 in FIG. 5. The opening of intake valve 18 appertaining tothe second partial period is denoted in FIG. 6 by the number 6.1. Thisopening lasts for only a relatively short time, since for oxidizing theresidual gas resulting from the preceding combustion of the combustionchamber charge, no new charge of the combustion chamber is necessary.The new charge of the combustion chamber with fresh gas takes place bythe wider valve opening pulse 6.2 in FIG. 6. This opening pulse 6.2corresponds, in this context, to the abovementioned first partialperiod. Approximately between the two openings of intake valve 18,exhaust valve 36 is opened for expelling the residual gases that havebeen combusted and post-oxidized by the secondary air.

The opening pulse for exhaust valve 36 is shown by curve 7.1 in FIG. 7.For this reason, the internal cylinder pressure remains within the rangeof the exhaust gas back pressure even after the closing of the intakevalve. In this context, it is assumed that the exhaust gas back pressurecorresponds approximately to the environmental pressure, which alsoprevails in the intake manifold. At point t3, exhaust gas valve 36 isclosed, and at time t2 the intake process is also ended by closingintake valve 18. On the assumption that the combustion chamber charge isset via the intake valve and that the desired charge is relativelysmall, even a part of the downwards movement of piston 14 is sufficientfor drawing in the desired charge. In this context, a pressure that isas high as possible in the intake manifold is advantageous. In anaturally aspirated engine this is approximately the environmentalpressure. Therefore, at time t2, piston 14 has not yet arrived at itsbottom dead center.

The further movement of piston 14 in the direction of its bottom deadcenter enlarges combustion chamber 12 if valves 18, 36 are closed, andthereby leads to an additional reduction in the pressure in thecombustion chamber. Thereafter, the piston runs again in the directionof its top dead center, which permits the pressure in the combustionchamber to rise correspondingly. This rise after the temporaryadditional falling off is illustrated in FIG. 5, in curve section 5.3.

The solid line in FIG. 8 shows the corresponding residual gas content incombustion chamber 12, and the dashed line in FIG. 8 shows thecorresponding fresh air proportion. First of all, left of t1, there isonly residual gas from the combustion in the combustion chamber. At timet1, intake valve 18 is opened at low final combustion pressure. As aresult, no residual gas flows out of the combustion chamber, but freshgas flow into the combustion chamber. The two gas components react witheach other, which leads to a slight rise in the residual gas proportionat falling fresh gas proportion. Further along on the curve, bothcomponents fall off to a low value with exhaust valve 36 open, beforethe fresh gas proportion rises to its final value as a result of theopening intake valve 18. At time t2, this rise is closed off when intakevalve 18 is closed.

In FIG. 3, steps 3.8 to 3.12 correspond to the signal curves described.If the query in 3.8 is answered yes, i.e. if the cylinder pressureundershoots the intake manifold pressure at the end of the combustionstroke, in the second partial period the intake valve is activated toopen in step 3.9. Step 3.10 represents the opening of the exhaust valvecorresponding to curve 7.1 in FIG. 7, and step 3.11 represents theopening of the intake valve in the first partial period corresponding tocurve path 6.2 in FIG. 6. Step 3.12 represents a return to the mainprogram.

The exemplary method according to the present invention is able to beused both for naturally aspirated engines and for pressure-chargedengines. In turbocharged engines secondary air metering may be provided,according to the exemplary method of the present invention presentedhere, even in the case of larger cylinder charges, since the pressure inthe intake manifold is greater for turbocharged engines, and thesecondary air supply, according to the exemplary method and/orembodiment of the present invention, via an opened intake valve at theend of the combustion stroke presupposes a certain pressure drop at theintake valve. The exemplary method according to the present invention isparticularly suitable for internal combustion engines/piston engineshaving direct gasoline injection, as shown in FIG. 1. In the case ofmanifold injection, the wall-applied fuel film on the inside wall of theintake manifold could prove to have a disruptive effect.

1. A method for controlling the opening of at least one intake valve of a combustion chamber in a periodically working piston engine, the method comprising: opening the at least one intake valve for charging the combustion chamber during a first partial period of a working period of the piston engine; and opening the at least one intake valve of the combustion chamber during a second partial period of the working period, wherein the second partial period begins in an expansion phase and has no overlap with the first partial period; wherein air from an intake manifold reaches the combustion chamber via the opening of the at least one intake valve during the second partial period of the working period.
 2. The method of claim 1, wherein the second partial period begins before a bottom dead center of a piston allocated to the combustion chamber.
 3. The method of claim 2, wherein the second partial period begins when a pressure on a side of an intake valve facing the combustion chamber undershoots a value of a pressure on a side of the intake valve facing away from the combustion chamber.
 4. The method of claim 1, wherein at least one of a length of the second partial period and an extent of the opening of the intake valve is a function of an operating characteristic variable of the piston engine.
 5. The method of claim 1, wherein the charging of the combustion chamber is limited by an early closing of the intake valve, and the openings are performed at an intake manifold pressure that is as high as possible.
 6. The method of claim 1, wherein the openings are performed below a threshold value for a combustion chamber charge.
 7. The method of claim 1, wherein at least one first intake valve is opened during the first partial period, and at least one second intake valve is opened during the second partial period.
 8. A control unit for controlling the opening of at least one intake valve of a combustion chamber in a periodically working piston engine, comprising: a first arrangement to open the at least one intake valve for charging the combustion chamber during a first partial period of a working period of the piston engine; and a second arrangement to open the at least one intake valve of the combustion chamber during a second partial period of the working period, wherein the second partial period begins in an expansion phase and has no overlap with the first partial period; wherein air from an intake manifold reaches the combustion chamber via the opening of the at least one intake valve during the second partial period of the working period.
 9. The control unit of claim 8, wherein the control unit increases an idling speed of the piston engine during the openings of the first and second partial periods.
 10. The control unit of claim 9, wherein the control unit shifts at least one switching point of an automatic transmission to a high rotary speed during the openings of the first and second partial periods.
 11. The control unit of claim 9, wherein the control unit operates the piston engine at a fuel/air mixture that is increasingly lean with an increasing combustion chamber charge during the openings of the first and second partial periods.
 12. A method for controlling the opening of at least one intake valve of a combustion chamber in a periodically working piston engine, the method comprising: opening the at least one intake valve for charging the combustion chamber during a first partial period of a working period of the piston engine; and opening the at least one intake valve of the combustion chamber during a second partial period of the working period, wherein the second partial period begins in an expansion phase and has no overlap with the first partial period; wherein the charging of the combustion chamber is limited by an early closing of the intake valve, and the openings are performed at an intake manifold pressure that is as high as possible.
 13. A method for controlling the opening of at least one intake valve of a combustion chamber in a periodically working piston engine, the method comprising: opening the at least one intake valve for charging the combustion chamber during a first partial period of a working period of the piston engine; and opening the at least one intake valve of the combustion chamber during a second partial period of the working period, wherein the second partial period begins in an expansion phase and has no overlap with the first partial period; wherein the openings are performed below a threshold value for a combustion chamber charge. 